Gap on an 850 with +20 ?

NORBECER said:

Found this article on the Norton Owner's Club site regarding determining wear without the use of instruments. It will tell you if you require a rebore, however it doesn't help determine if the cylinder is oval or not.

J.B. Nicholson - Modern Motorcycle Mechanics

Cylinder Block Measuring and Reboring:- Cylinder wear can be fairly accurately determined without micrometer equipment by placing a piston ring in the lower unworn end of the cylinder, measuring the gap with a feeler gauge and then shoving the ring with a piston to the top end of the ring travel in the cylinder and measuring the gap in this postion. The difference in joint gap measured at these two positions will represent approximately three times the cylinder diameter wear. For example, if the ring gap at the lower end is 0.010" and the top end measures 0.040", the difference of 0.030" circumference increase indicates approximately 0.010" diameter wear, and reboring and oversize piston fitting is indicated. Generally cylinder wear of over 0.008" calls for reboring for fully satisfactory results.

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The one problem with this is that the bore can wear out of round. This method won't give you that measurement.

NORBECER said:

dennisgb said:

If your new to rebuilding an engine then it is difficult to figure out. You'll get a lot of different opinions, all of them may work but I always err on the conservative side once I have an engine torn down. The amount of time is more valuable than the parts, and peace of mind comes into play. It looks like you need head work for sure. I would look at new pistons and possibly a rebore as there is some pitting in the cylinders. That might be okay, and even the existing pistons might be fine with new rings if the bores check out. I wouldn't chance it though.

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The head needs a complete over haul that's for sure, and trust me I would rather have the new parts as well. I've read far too often here on the Forum about bad re-bores and engines blowing up on their maiden voyages. Makes me nervous since +40 puts me one away from scraped barrels. I would prefer to go new pistons and rings with the present barrels if possible. Cheers

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I agree here, and even if the bore measured within specs and straight I'd want to hone it with a good cross hatch to seal in new rings as the bore finish as is doesn't look good to me. With the work you're going to do the head, I'd want that head sitting on perfect bores. Technically .040 over will bring the bores closer to the limit but with modern oils and probably the best future maintenance your bike will ever see, that limit will be far, far down the road, if it is ever reached.

A few years ago I was chatting with Herb Becker about my 650 SS, which is .060" over. It was renewed about 3,000 miles earlier, in part by Herb.
I asked if he knew of any good 650 barrels available as spares in the event I wore out the existing setup.
His reply was that with the components used it should run 60,000 miles before needing redo and that I would never wear out the existing setup. It appears he was correct, I might have 6,000 miles on the bike today.
The bike I use most has done just over fourty thousand miles in the last ten years, and that was a lot of riding. Even if I suddenly start riding the 650ss at those levels, the top end of the 650 should last 15 years or more.
He also pointed out that if something untoward did occur, it is fairly straightforward to simply sleeve the barrels and go back to standard bore. So I stopped worrying about wearing it out. Nowadays I worry more about NOT wearing it out!

Glen

NORBECER said:

concours said:

They look like mine did.. rust stained, but not rusty. Get a bright light and magnifying glass. :shock:

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So tell me what was your remedy :?: Inquiring minds would like to know.

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Some relevant reading here: norton-top-end-break-now-t14414.html

Many thanks to everyone for your helpful input. I will most likely go with a +40 re-bore. Not sure as to the make of piston, do I drop a wad of cash on GPMs or go the econo route with Hepolites?

NORBECER said:

Many thanks to everyone for your helpful input. I will most likely go with a +40 re-bore. Not sure as to the make of piston, do I drop a wad of cash on GPMs or go the econo route with Hepolites?

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I retained .020" oversize on my 850, the pistons and rings were trashed, but the bores surprisingly good. I did not de-glaze, just a deep clean and fitted new .020" Hepolites. Using good oil, 2 years later the bike has 140PSI in each cylinder, burns no oil (and no leaks either) on a recent 2,400kms east coast trip (Australia) the total oil consumption was 600ml, or 1 pint. Nothing wrong with Hepolites for stock motors.

GPMs do not have a good rep with my local club. They made some pistons in the 90s that were not cam ground and these resulted in a number of piston seizures. I still have a set in one bike, but one day will yank them and install low expansion pistons instead, just for peace of mind when riding it.

Glen

Thats a Carbon Build Up , but its not a ' Carbon Over the Sides Errodeing and scouring out the ring lands ' from appearances .
As the bores not perfect ( but Close - some'd argue the imperfections will retain lube incresing life ) .

YOU would MEASURE the Ring Clearances - as in feeler guage over &/or under a NEW Ring in the Top Land ( it wears most ) and see what the fit is , Within Spec ??

Generally , if the entire piston crown was covered with the debri , it wouldve left big grooves down to the top ring , built up in the Ring Land & gummed things up .

" , you use a dicarded ring to clear grit / deposits from ring lands ( where the Rings Go , so theyre ickle pretty perfect , and the wing wont schtick .

Mayas well get some life outve them , if the rig is the same radial width ( major Dimn. in cross section ) , the outer ( and inner ) edges arnt ridged ( you could stone it off ! )
and theyre original QUALITY items like Hepolite , with matching diameters free - Not Overheaten , putting cheap shitty ones in instead would be retrograde .

Light Double Cross Hatch Hone to Reseat & Bobs your uncle .

Photo shows loss of ring oil control which dissolves carbon and tends to detonate slightly blasting surfaces clean but leaving unburnt carbon to collect just beyond. Carbon is harder than metals so rich mixture wash off oil in bores plus a grinding compound and leave drier looking deposits.

NORBECER said:

Found this article on the Norton Owner's Club site regarding determining wear without the use of instruments. It will tell you if you require a rebore, however it doesn't help determine if the cylinder is oval or not.

J.B. Nicholson - Modern Motorcycle Mechanics

Cylinder Block Measuring and Reboring:- Cylinder wear can be fairly accurately determined without micrometer equipment by placing a piston ring in the lower unworn end of the cylinder, measuring the gap with a feeler gauge and then shoving the ring with a piston to the top end of the ring travel in the cylinder and measuring the gap in this postion. The difference in joint gap measured at these two positions will represent approximately three times the cylinder diameter wear. For example, if the ring gap at the lower end is 0.010" and the top end measures 0.040", the difference of 0.030" circumference increase indicates approximately 0.010" diameter wear, and reboring and oversize piston fitting is indicated. Generally cylinder wear of over 0.008" calls for reboring for fully satisfactory results.

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I was curious to see how my barrels would measure up using this method:
Old top ring at 3/4 inch below the top of the cylinder, gap came in at .018
Old top ring at the base of the barrel , gap came in at .014....if I do the division as per the above calculation the wear is negligible.

Any comments :?:

Spend the money on oversize pistons and a rebore and get the final hone to the mim. clearance and your bore will last you forever if you keep running good clean oil, when I did my rebore many many years ago with orginal 40+ Hepilight pistons I did my final hone at 002th, nomaly they would be 004th but I did mine at 002th and run the first 100 miles on a very cold night, I froze my balls off but was worth it and never had any problems, I have done well over 70,000 miles on this bore and when I had to replace my crank cases on the last rebuild over 4 years ago all I did was to replace the rings and a very light hone, my motor is still tight, don't blow any smoke at all and my mates still can't kick it because of the compression, just the way I like it.

Ashley

ashman said:

Spend the money on oversize pistons and a rebore and get the final hone to the mim. clearance and your bore will last you forever if you keep running good clean oil, when I did my rebore many many years ago with orginal 40+ Hepilight pistons I did my final hone at 002th, nomaly they would be 004th but I did mine at 002th and run the first 100 miles on a very cold night, I froze my balls off but was worth it and never had any problems, I have done well over 70,000 miles on this bore and when I had to replace my crank cases on the last rebuild over 4 years ago all I did was to replace the rings and a very light hone, my motor is still tight, don't blow any smoke at all and my mates still can't kick it because of the compression, just the way I like it.

Ashley

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Thanks Ashley, I will most likely go with the +40. I was recommended a shop here in Montreal by a small reputable BMW shop, Lemoyne Moto on the south shore.